What can be said about the Doom series that hasn't already been said? These games are immensely satisfying, and it's hard to pick just one. However, there's so much disparity between each game, particularly between 3 and the first two, that they really have to be looked at as separate entities in this case. Doom 3 does uphold the tradition of having Earth threatened by the minions of Hell, but this time, teleportation experiments conducted by a military-fortified corporation on Mars have accidentally opened a gateway, releasing demons who are intent on heading towards Earth.
Even though the thought of demons and the walking dead taking over a military base on Mars and piloting stolen spacecraft to earth sounds moderately hilarious ("Hey, Beelzebub, can you drive a manual transmission?"), the game unfolds at such a pace that there isn't much time to contemplate the realities, as one of the humans associated with a visiting team is revealed to be cooperating with Hell to facilitate the invasion. Loading with exploding guts and blood splatters, gameplay is about what one would expect for a Doom game. Gory, satisfying, and not without a touch of black humor.